The purpose of this project is to investigate how responses to stress influence the genesis of ventricular arrhythmias, and their detection by currently available diagnostic methods. Subjects in the study will be patients who have manifiested nonsustained ventricular tachycardia during ambulatory electrocardiographic monitoring. Their cardiac disease will be defined by noninvasive testing and right heart catheterization. Psychosocial variables will be assessed by psychometric and demographic questionnaires. Cardiac electrical instability will be evaluated by quantifying ventricular arrhythmias recorded during ambulatory monitoring and electrophysiologic studies. Stress response patterns will be quantified by measuring cardiac and neuroendocrine (cortisol, growth hormone, free fatty acids and catecholamines) responses to exercise and stressful interviews conducted during cardiac monitoring and electrophysiologic study. Objectives of the study are as follows: 1) to measure neuroendocrine responses to exercise, a stressful interview, anad electrophysiologic studies; 2) to verify that individual differences in neuroendocrine responses to such stresses correlate with baseline psychosocial variables; 3) to relate arrhythmia susceptibility to stress response patterns and underlying heart disease; 4) to quantify day-to-day variability of ventricular arrhythmias induced during electrophysiologic studies, and observed during ambulatory monitoring in and out of hospital; 5) to correlate day-to-day arrhythmia variability with psychologic and neuroendocrine stress response patterns; and 6) to correlate exercise-induced arrhythmias and stress response patterns with vulnerability to electrophysiologic induction of ventricular arrhythmias. Data from these studies should help clarify the roles of stress and underlying heart disease in ventricular arrhythmogenesis. Knowledge of how these factors influence detection and variability of arrhythmias by currently available techniques will help define the limitation of these methods, and facilitate selection of the proper tool for managing specific patients. Identification of factors predictive of arrhythmia induction by a stressful interview will allow selection of patients in whom this stimulus may improve the yield and reproducibility of detection method. Finally, definition of patient characteristics which correlete with susceptibility to serious ventricular arrhythmias may improve individualization of therapy and facilitate selection of patients for future studies into the prevention of sudden death.